Selective heating and drawing of plastics



April 5, 1966 J. LEVEY ETAL SELECTIVE HEATING AND DRAWING OF PLASTICSFiled June 29, 1962 1 ab 9 e h s s t e INVENTORS. LEVEY JOHN April 5,1966 J. LEVEY ETAL 3,244,779

SELECTIVE HEATING AND DRAWING 0F PLASTICS Filed June 29, 1962 4Sheets-Sheet 2 tfomv LEvEY COHA/ Pyx. 0N7

INVENTORS.

April 1965 J- LEVEY ETAL 3,244,779

SELECTIVE HEATING AND DRAWING OF PLASTICS Filed June 29, 1962 4Sheets-Sheet 5 (TO/4N LE VEY II'OHN Pu. ANT

INVENTORS.

BYM07IW April 5, 1966 J. LEVEY ETAL 3,244,779

SELECTIVE HEATING AND DRAWING 0F PLASTICS Filed June 29, 1962 4Sheets-Sheet 4 J INVENTORS.

(To /xv LE VEY JOHN P yz. 9N7

United States Patent Ofiice 3,244,779 Patented Apr. 5, i965 3,244,779SELECTIVE HEATENG AND DRAWING F PLASTECS John Levey, 4524 Beeman Ave,Studio (Iity, Calif., and John Pylant, 16317 Lassen St, Sepulveda,Calif. Filed June 29, 1962, Ser. No. 206,266 Claims. (Cl. 264-89) Ingeneral, the present invention involves methods for pressurethermoforming hollow shaped parts from a sheet of thermoplastic materialhaving walls of controlled thickness distribution. More particularly,the methods of the present invention relate to heating and stretching acontinuous sheet of thermoplastic material to form hollow containerstherefrom wherein the heating and stretching are adapted to permit thecontrolled expansion of the sheet portion forming the walls of saidhollow containers and subsequently filling, sealing, and separating saidhollow containers.

The thermoforming of generally concave, hollow shaped parts, such ascontainers, from sheets of thermoplastic material, usually employing avacuum, is Well known in the art of plastics fabrication and otters aneconomical and rapid method for fabricating plastic containers fromsheets without the use of high pressures and temperatures required forinjection molding. The general procedure followed in vacuumthermoforming processes is to clamp a sheet of thermoplastic resin in aframe, soften it by heating (conveniently by means of radiant heat),remove the heat source, press the softened sheet tightly over thesurface of a warm die having one or more hollowed-out cavities in theshape of the desired article and then drawing the sheet down into thedie surface by evacuation of the air trapped between the sheet and thedie. The thermoplastic resin is then set in the shape of the die bycooling which is accomplished by heat transfer both to the warm die andto the atmosphere.

The process of thermoforming as described above has been relativelysuccessful in forming shallow containers which have a depth-tobasediameter ratio of less than about /3. As is well known in the art, theterm base diameter refers to the maximum linear dimension through thecenter of the base irrespective of the particular shape of the base.However, where it has been necessary to draw the thermoplastic sheetinto deep cavities, particularly those in which the depth-to-basediameter ratio is greater than about /2, such prior art vacuumthermoforming processes have been unsatisfactory. In such cases, theoperation of the unmodified process of vacuum thermoforming results inarticles with very thin bottoms and thin lower walls due to the greaterstretching of the softened thermoplastic sheet in those areas.Consequently, the prior art has developed numerous processes generallydesignated as plug-assist thermoforming processes wherein a tapered,blunt-nose plug is employed to push the sheet down into the die.However, such plug-assist thermoforming processes require much morecomplicated machinery and careful control to obtain the desired results.In addition, vacuum thermoforming has a number of other disadvantages.For example, the use of radiant heating slows down the process as awhole and requires that the heating and forming steps be formed inseparate steps. Also, the use of a vacuum to form the container from thesheet greatly limits the available pressure differential which may beused during the forming operation.

Consequently, the objects of the present invention include methods forthe production of hollow shaped parts from a sheet of thermoplasticmaterial having walls of controlled thickness distribution withoutrequiring the complicated, expensive apparatus and methods of plugassistthermoforming;

Another object of the present invention is a simple, fast method ofpressure thermoforming a hollow container from a sheet of thermoplasticmaterial without the limitations of the vacuum thermoforming process.

Still another object of the present invention is an inexpensive, simpleapparatus for pressure thermoforming hollow containers from a sheet ofthermoplastic material having a depth-to-base diameter ratio of greaterthan /2 and having walls of controlled thickness distribution.

Still another object of the present invention is a simple, inexpensiveapparatus for continuous production of hollow containers having walls ofcontrolled thickness distribution from a continuous sheet ofthermoplastic material.

Other objects and advantages of the present invention will be readilyapparent from the following description and drawings which illustrateexemplary embodiments of the present invention.

In general, the present invention involves methods for the production ofhollow shaped parts having walls of controlled thickness distributionfrom a sheet of thermoplastic material. The methods and apparatus areadapted to heat and stretch portions of said sheet to permit thecontrolled expansion of the sheet portion forming the walls of thehollow shaped parts.

In order to facilitate understanding of the methods of the presentinvention, reference will now be made to the appended drawings of thespecific embodiments of the present invention. Such drawings should notbe construed as limiting the invention which is properly set forth inthe appended claims.

FIG. 1 is a side view of the complete apparatus for continuousproduction of hollow containers having walls of controlled thicknessdistribution from a continuous sheet of thermoplastic material.

FIG. 2 is a top view of the apparatus shown in FIG. 1.

FIG. 3 is a cross-sectional view of the apparatus shown in FIG. 1 takenalong the lines of III-Ill of FIG. 1.

FIG. 4 is an enlarged view of a portion of FIG. 3 showing a molding unitfor a single hollow container during the forming of a hollow nodule.

FIG. 5 is the same view as shown in FIG. 4 showing the hollow containerforming portion of the thermoforming method.

FIG. 6 is a cross-sectional view of FIG. 3 taken along the lines VL-VIof FIG. 3.

FIG. 7 is an enlarged cross-sectional view of FIG. 1 taken along thelines VII-VII of FIG. 1.

FIG. 8 is a cross-sectional view of FIG. 1 taken along the linesVIII-VIII of FIG. 1.

PEG. 9 is a cross-sectional view of FIG. 1 taken along the lines lX-IXof FIG. 1.

FlG. 10 is a cross-sectional view of FIG. 2 taken along the lines X-X ofFIG. 2.

FIG. 11 is a sectional view of FIGS. 1 and 10 taken along the lines XlXlof FIGS. 1 and 10.

FIG. 12 is a perspective view of a typical container produced by theapparatus shown in FIGS. 1-12.

In FIGS. 1-12 the preferred embodiment of the present invention isillustrated showing the continuous production of hollow containershaving walls of controlled thickness distribution from a continuoussheet of thermoplastic material. The apparatus shown in FIGS. 1l2,generally in dicated as 1, includes a molding unit 10 adapted to heatand stretch portions of a thermoplastic sheet 2 to form hollowcontainers 3 therein. The hollow containers 3 formed in sheet 2 thenpass to a filling unit 3% adapted to fill them with a predeterminedamount of material. The filled containers then pass through a sealingunit 40 which is adapted to tightly cover them with a second sheet ofthermoplastic material. The sealed, filled containers then move to apunching unit 50 preferably adapted to separate such containers from thesheet of thermoplastic material. Finally, a transfer unit 66 is adaptedto move the continuous sheets 2 of thermoplastic material at periodicintervals so that each sheet portion in which the hollow con tainers 3are formed moves in sequence in operative association with said moldingunit 10, filling unit 30, sealing unit 46, and punching unit 56.

Apparatus 1 is fed a continuous sheet 2 of the thermoplastic materialfrom a roll 4. Constant tension is maintained on sheet 2 at all times bymeans of weight 5 rotatably mounted on arm 6 which is in turn rotatablymounted on pivot 7. When transfer unit 66 moves sheet 2 forward, weight5 initially moves upward to maintain constant tension on sheet 2. Thenweight 5 descends to its lower position causing roll 4 to unwind.

The molding unit 16 of apparatus 1 includes molding head platen 11having a plurality of recesses 12 therein adapted to receive theexpansion of the thermoplastic sheet 2 stretched across its lowersurface 13. The surfaces 14 of recesses 12 are shaped to contact theexpanded sheet 2 in a controlled sequence when sheet 2 is expanded intorecess 12. The molding head platen 11 includes conduit means 15 forcommunicating fiuid pressure to recess 12. Molding head platen 11 alsoincludes a heating means 16 for heating the molding head platen 11 to apredetermined temperature. A molding base platen includes an upper plate17 having a plurality of cavities 18 therein aligned with the recesses12 of head platen 11. The surfaces of the cavities 18 shape theexpansion therein of the thermoplastic sheet 2 to form the hollowcontainers 3. The molding base platen also includes a lower plateforming the bottom surface of cavities 18 and having conduit means 19for communicating fluid pressure to the cavities 18. Molding base platen17 and 20 are supported by a base plate 21. Base platen 17 is supportedby a cooling plate 20 and a base plate 21.

Operatively associated with the molding head platen 11 and molding baseplatens 17 and 20 are clamping means 22 for moving said platens togetherinto sealing relationship with the sheet 2 of thermoplastic materialtherebetween. Clamping means 22 includes four independent gripping means23 located around the perimeter of the head and base platens 11 and 17,respectively. The gripping means 23 are adapted to clamp the edgeportions of said platens together under the same pressure and therebyeffectively compensate for deviations from the horizontal of the matingplaten surfaces. Gripping means 23 are comprised of a piston 24 in acylinder 25 which actuates a piston rod 26. Clamping means 22 alsoinclude a head plate 27 which is attached to piston rods 26 and whichrests upon the heating means 16. Operatively associated with the platenconduits 15 and 19 is a conventional pump means (not shown) forestablishing fluid pressure in said recess and cavity.

The filling unit 36 adapted to fill the hollow containers 3 includes aplurality of ports 31 with each port aligned with a corresponding hollowcontainer 3. Forts 31 are fed by conduits 32 into which is admitted thefiuid feed material under pressure. The flow from conduit 32 of feedmaterial to port 31 is controlled by a valve 33. The position of valve33 is in turn controlled by a piston Se in a cylinder 35. Valve 33 isopened by fluid pressure through pipe 36 on the underside of piston34and it is closed by the compression of spring 37 on the upper side ofpiston 34. The force exerted by spring 37 on the upperside of piston 34is regulated by a threaded screw 38 with a spring support 39 mountedthereon. Initially, the opening of valve 33 is determined for all ports31 by the fluid pressure in line 36. However, because of the individualvariation in position and pressure drop for each of the ports 31 thethreaded screw 38 permits the flow to each of the ports to be controlledindividually.

The sealing unit 46 is adapted to tightly cover the filled containerswith a second sheet of plastic material, such as Mylar. Sealing unit 40includes a sealing base platen 41 having cavities 42 therein forreceiving each of the filled containers 3 and a sealing head platen 4-3mounted above the sealing base platen 41. Sealing base platen 41 restsupon a base plate 44. Sealing base platen 41 and sealing head platen 43are brought together in sealing relationship by means of sealingclamping means 45 having the same construction as molding clamping means22. A second sheet 46 of thermoplastic material is unrolled from a roll47 and covers the top surface of sheet 2 when the sealing base platen 41and sealing head platen 43 are clamped together in sealing relation.While in such sealing relation, heat is applied through the sealing headplaten 43 in the conventional manner so that the second thermoplasticsheet 46 forms a tight cover over the filled containers 3.

As illustrated, the punching unit 56 is adapted to separate the sealed,filled containers 3 from the continuous sheet 2 of thermoplasticmaterial. The punching unit 50 includes a base die 51 having apertures52 therein aligned with each of the sealed, filled containers 3. Basedie 51 is supported by a base support plate 53 having holes 54 thereinwhich are aligned with the apertures 52 in base die 51. Mounted abovebase die 51 is a head die 55 having die cutters 56 mounted thereonaligned with the apertures 52 in base die 51. Head die 55 is mounted ona clamping means 57 which is the same as clamping means 22. Properalignment of the sealed, filled containers 3 in punching unit 50 isinsured by switching means 58 whose contact arm 56' is actuated by oneof the lead containers 3. When arm 58' is actuated, it rotates away frompunching unit 56 and stops the transfer unit 60. The next movement ofthe transfer unit then rotates contact arm 58' back into position forthe next set of sealed, filled containers 3. When the head die 55 andthe base die 51 are moved together by clamping means 57 the sealed,filled containers 3 are punched out and dropped on to a conveyor 59 forsubsequent handling operations.

Transfer unit 60 is adapted to move the continuous sheets 2 and 46 atperiodic intervals so that the sheet portions in which the hollowcontainers 3 are formed and which seal the filled containers are movedin sequence in operative association with the molding unit, fillingunit, sealing unit and punching unit. Transfer unit 66 includes amovable clasping unit 61 which is slidably mounted on bars 62 and ismoved by a piston and cylinder between a position adjacent to punchingunit 56 and a position adjacent to stationary clasping means 66 as shownin FIG. 10. Movable clasping unit 61 includes a vise 63 actuated bypiston and cylinders 64 which move the upper vise arm 63 into and out ofgripping position with respect to lower vise arm 63". Transfer unit 60also includes a stationary clasping means 66 having a vise 6'7 actuatedby piston and cylinders 68 in the same fashion as the sliding clampingmeans 61. When the moving clamping means 61 moves toward the stationaryclamping means 66, its vise 63 is closed to tightly grip the continuoussheets 2 and 46 while the corresponding vise 67 in the stationaryclasping means 66 is open to permit the continuous sheets 2 and 46 topass freely therebetween. When the clasping means 61 reaches theposition adjacent to the stationary clasping means 66, its vise 63 thenopens while vise 67 of stationary clasping means 66 is closed. Movableclasping means 61 then returns to its initial position with its vise 63open so that the continuous sheets 2 and 46 may slide freelytherebetween. During such movement of clasping means 61, the continuoussheets 2 and 46 are maintained in stationary position by the closed vise67 of the stationary clasping means 66.

Conventional control means are operatively associated with the apparatusand its molding unit, filling unit, sealing unit, punching unit, andtransfer unit to operate the apparatus and each of said units in propersequence with respect to each successive sheet portion. A variety ofwell known control systems may be used with said apparatus and its unitsand such systems are not part of the present invention. However, theessential features of their construction will be obvious to one skilledin the art in view of the following discussion of the operation of theapparatus 1.

In operation of apparatus 1, the transfer unit 60 moves a new portion ofcontinuous sheet 2 into position in molding unit 10, while molding headplaten 11 is in its raised position. Clamping means 22 then moves thehead and base platens together in sealing relationship by introducingfluid, i.e. gas or liquid, above and exhausting it below pistons 24 incylinders 25. After head platen 11 has been clamped sufficiently tightlyagainst the base platen 13 to prevent leakage therebetween, air is thenintroduced under pressure into conduit 19 and exhausted through conduit15. Preferably, the flow of fluid through each of the individualcavities 18 in the base platen 1'7 and 20 is controlled by individualflow orifices whose opening may be regulated by a valve; however, allcavities 18 may be fed through a single conduit 19 as shown in FIG. 3.Fluid pressure in cavity 18 may be built up at a controlled rate andmaintained for a predetermined time period while the fluid pressure inrecess 12 is merely exhausted to the atmosphere or decreased in asimilar controlled fashion. For example, when molding a polystyrenesheet of about 0.01 inch thickness and using a heater temperature ofabout 300 F., pressure may be built up to about 40 p.s.i.g. in about 2to 4 seconds. As fiuid pressure is exerted on the thermoplastic sheet 2it is stretched to form a hollow nodule therein which nodule is receivedby recess 12.

The molding head platen 11 is preferably maintained at a uniformpredetermined temperature by heater 16 throughout the operation ofapparatus 1. Consequently, the sheet portion surrounding the base of thehollow nodule is heated throughout the entire time period that fluidpressure is exerted in cavity 18 so that its temperature is raised to apoint at which the thermoplastic material is easily forrned. Thesurrounding sheet portion therefore expands inwardly due to such heatingand stretching to form the portion of the side walls of the noduleadjacent to its base. The central portion of the hollow nodule is thenforced upward in contact with the surface 14 of recess 12 in a sequencewherein the lower portion of the side walls of the nodule contact thesurface 14 first and then remaining portions contact the surface 14 in asequence dependent upon the pressure in cavities 18 and the temperatureof the surface 14. Consequently, most of the surface of the side wallsis heated for varying time periods shorter than the predetermined timeperiod With the first period being inversely proportional to thedistance from the base of the hollow nodule toward the top wall of thenodule and the side walls are expanded by such heating and stretchingproportional to their heating time period. In other Words, the timeperiod for heating the various side wall portions is decreased as thedesired amount of stretching of the side walls is decreased. The topwall of said hollow nodule is heated for a time period shorter than thepredetermined time period with such time period being inverselyproportional to the distance from the base of said hollow nodule. Ifdesired, the time period for the top wall of the hollow nodule may bereduced to zero when no stretching of the top wall is desired.Similarly, a portion of the side wall may substantially not be heated byhaving a second recess in the side Wall to prevent cont-act therewiththe said portion of the side wall of the nodule. Even when the top wallof the nodule is heated to some extent, the central portion of thehollow nodule, i.e. the top wall and the upper portion of the sidewalls, will not become substantially thinner since the thermoplasticsheet stretches to cover the entire surface 14 of recesses 12 before thecentral portion is sufficiently hot to stretch substantially.

Fluid pressure is then introduced into cavity 12 through conduit 15 andexhausted from cavity 18 through conduit 19. Such reversal of fluidpressure reverses the hollow nodule to form a hollow container in cavity18 with the inner walls of the hollow nodule forming the outer walls ofsaid container. Initially, during this process, the central portion ofthe container resists stretching more strongly than the portion of theside walls adjacent to its rim because the central portion is not as hotas such rim portion. Thus the hot rim portions of the container willstretch first, but they then contact the walls of cavity 18 first andbecome cooled thereby so that further stretching is prevented. Thussubsequent stretching of the container is confined to the heated centralportion that has not as yet touched the surface or" cavity 18. In thisway the bottom wall and side walls of the container are stretched toform a container having walls of controlled thickness distribution.

Fluid pressure is then exhausted from recess 12 through conduit 15 andthe head platen 1:1 is raised by clamping means 22. Transfer means 60then moves the hollow containers 3 to the filling unit 30. The hollowcontainers 3 are then filled by the filling unit 3t) while a second setof containers 3 are formed by molding unit 10. The filled containers 3are then moved by transfer unit 61) to the sealing unit 4% where theyare sealed 'While the second set of containers is filled by unit 3t} anda third set of containers is formed by molding unit 10. The sealed,filled containers 3 are then separated by punching unit 50 while thesecond set of containers is sealed by sealing unit 4%, the third set ofcontainers is filled by filling unit 30, and a fourth set of containersis formed by molding unit 10.

In the methods of the present invention it should be noted that the rimof the container, i.e. the base of the initially formed hollow nodule,is preferably circular, although it may be of any shape, such asasquare, a rectangle, and etc. In the preferred embodiment of theapparatus of the present invention the mouth of the recess in themolding head platen is preferably larger than the mouth of the cavityand the molding base platen in order to facilitate the removal of airfrom the recess and the expansion inward of the adjoining sheet portion.Where it is desired to not stretch a certain portion of the top or sidewall of the resulting container, e.g. where a sign or a decoration hasalready been printed on the fiat sheet, the corresponding portion of thesurface of the recess in the molding head platen may he pitted toprevent such portion of the sheet from becoming substantially heated.Alternatively, such area may he covered by a dish of material having lowheat conductivity to prevent substantial heating of that portion of thethermoplastic sheet, such as described in our copending applicationentitled Differential Heating and Drawing of Plastics being filedconcurrently here-with. If it is desired to heat the whole surface ofthe hollow nodule for substantially the same period of time, the fluidpressure in the cavity in the mold ing base platen may be increased veryquickly so that the time lag involved for the top wall of the nodule tocontact the depth of the recess in the molding head platen become-sinsignificant.

It should be noted that many thermoplastic materials may be used in theprocess of the present invention, in cluding such common ones aspolystyrene and the acrylic resins. In the case of the polystyreneresins, it should be noted that the biaxial stretching of the presentinvention improves the flexibil-ty and toughness of the resultingcontainer walls.

As set forth in the illustrated specific embodiment, the apparatusincludes a molding unit, filling unit, sealing unit, punching unit, andtransfer unit operatively connected into the single integral structure.Initially it should he noted that such structure may be enclosed in ahood so that the entire operation is conducted under an inertatmosphere, such as nitrogen. Such handling permits the packaging offoods so that they will retain their freshness in the resulting sealedcontainers for sub-stantially longer periods of time. However, themolding unit of the present invention is adapted to be utilized in manyother combinations. Thus the filling unit, sealing unit, and punchingunit may each be adapted to be physically removed from the apparatus orto be rendered inoperative. In such apparatus, the control system wouldbe designed so that the molding unit forms the master control sectionwith each of the other units being connected thereto by jacks or plugs.With such variation of the present invention, for example, the moldingunit could be used solely with the punching unit to form emptycontainers. It should also be noted that other types of filling,sealing, punching and transfer units may be utilized in connection withthe molding unit of the present invention. For example, the filling unitmay be one which is adapted to fill the containers with nuts and boltsor cereal, rather than a fluid mixture, such as cottage cheese. Also,the sealing unit may be adapted to fit individual covers on thecontainers by feeding them from a magazine and putting them in placewith a plunger mechanism. In addition, while the whole apparatus mayutilize a continuous sheets, if desired, separate sheets may also beused for each set of containers. Also, any shaped part may be formedfrom a sheet of material in addition to containers, such as hollowconcave or convex shapes.

There are many features in the present invention which clearly show thesignificant advance the present invention represents over the prior art.Consequently, only a few of the more outstanding features will bepointed out to illustrate the unexpected and unusual results attained bythe present invention. One of the features of the present invention isthe preforming of a hollow nodule prior to the forming of the hollowcontainer to be produced wherein the sheet portions surrounding thenodule are expanded (inwardly to form a portion of the side walls ofsuch nodules adjacent to its base. Also, the side walls and top of suchhollow nodule are heated and stretched in a fashion so that the upperrim portions of the resulting containers are first initially formed andthen the bottom and side portions adjoining the bottom are subsequentlyformed with a controlled amount of stretching in each case. Thus, forexample, the rim portions of the resulting container are heated for apredetermined period of time while the remaining portions of thecontainer are heated for shorter time periods, with the shorter timeperiods being inversely proportional to the distance from the rim ofsaid resulting container toward the bottom of the container.

Another feature of the present invention is the utilization of fluidpressure to form the hollow containers and to heat the sheet beingmolded by contact with a heated surface. Such feature permits muchhigher pressure differentials for rapid forming of the hollow containersand achieves more economical and rapid heating of the sheet ofthermoplastic material. In addition, pressure heating and forming asillustrated can be done in a single operation which eliminates anadditional step in the usual plastics forming process and apparatus.However, probably most important is the versatility of such featuresince molding can be done with equal facility with male or female moldsand the heater may be either above or below the sheet of plastic beingformed. In the case of vacuum thermoforming, it is necessary that theheater be located above the sheet since as the sheet is heated it sagsand would contact the heater. An example of the versatility afforded bythis feature would be the use of male molds, rather than the femalemolds illustrated in the drawings to form the containers of the presentinvention. In such case, the male molds should project downwardly sothat the containers being formed are upright and ready to be filled inthe succeeding filling unit. When the base platen containing the malemold projects downwardly, the head platen containing the heater must bebelow it and the sheet is then forced upward to form the containersafter the initial heating period. With such mole mold, the recesses inthe head platen should preferably have an annular shape so that the topwall of the nodule normally contacts the surface of the sheet for asubstantial time period and the sheet is stretched to give a resultingcontrolled wall thickness when formed on the male mold.

Another feature of the present invention is the utilization of a splitmolding base platen having an upper and lower plate. As illustrated, theupper plate forms the side Walls of the hollow container whfle thebottom plate forms the bottom wall. Such feature permits the mold to bemade much more simply particularly where unusual bottom wallconfigurations are desired, eg the bottom may be convex upwardly with atrade insignia formed on it. Also, such feature facilitates the formingof the conduits for communicating fluid pressure to the cavity in thebase platen since they may be merely grooves or a single, wide, shallowrecess in the upper surface of the bottom plate.

Another feature of the present invention is the utilization ofindependent gripping means around the perimeter of not only the moldingunit but also the sealing and punching units. For example, in the caseof the. molding unit, such independent gripping means around theperimeter of the molding head and base platens insures a uniformpressure around the edges when the platen surfaces are not initiallyparallel. Thus leakage is prevented without the necessity of excessiveclamping pressures. In addition, if one of the platens is placed at anangle to the base of the molding unit for special molding operations,then the other platen will automatically adapt to the change to give auniform seal.

Still another feature of the present invention is the utilization of aplurality of filling units utilizing a single pressure to give the flowof the fluid feed material combined with regulating means forindividually controlling the flow of feed material to each container.

Another feature of the present invention is a switching means in thepunching unit which compensates for the stretching of the sheet as awhole during the passage of the containers through each of the units ofthe present invention. Such switching unit insures the proper alignmentof the containers when the final cutting operation is performed.

It will be understood that the foregoing description and drawings areonly illustrative of the present invention and it is not intended thatthe invention be limited thereto. Many other specific embodiments of thepresent invention will be obvious to one skilled in the art in view ofthis disclosure. All substitutions, alterations and modifications of thepresent invention which come Within the scope of the following claims orto which the present invention is readily susceptible without departingfrom the spirit and scope of this disclosure are considered part of thepresent invention.

We claim:

1. The method forming a hot ductile sheet of thermoplastic material intoa three dimensional shape comprising forming the material into a cavitymold including the steps of placing the material over the mouth of acavity mold, providing a heat source over the mold, applying pressure tocause an area of the material to move upwardly from the cavity mold soas to progressively come in contact with surfaces of the heat source,and then applying pressure to force the said area of the materialdownward to conform to the shape of the cavity mold whereby the heatingof the area as it is moved upwardly is determined by its contacting ofthe heated surfaces so that there is greater heating of the areaadjacent the rim of the cavity mold whereby a formed article is realizedhaving bottom and side walls of controlled thickness distribution.

2. A method as in claim 1 wherein the forming pres.- sure is applied ata controlled rate to cause the said area to form upwardly progressivelyso as to progressively contact surfaces of the heat source.

3. A method as in claim 2 wherein the pressure for causing the materialto form to the cavity mold is applied at a controlled rate as to causethe material to progres sively contact the interior side walls of thecavity mold.

4. A method as in claim 1 including the step of forming the said area ofmaterial in the direction away from the cavity mold in a generally domeshaped nodule formation.

5. A method as in claim 1 wherein the central portion of said area issubstantially not heated.

References Cited by the Examiner 1 0 2,670,501 3/1954 Michiels 18562,702,411 2/1955 Winstead 18-19 2,917,783 12/1959 Olson et a1. 18-562,949,713 8/1960 Vogt 53-29 2,967,328 1/1961 Shelby et a1. 18-192,970,444 2/1961 Rohdin 5329 2,985,915 5/1961 Winstead 264-327 XRFOREIGN PATENTS 741,040 11/1955 Great Britain.

ROBERT F. WHITE, Primary Examiner.

MORRIS LIEBMAN, ALEXANDER H. BROD- MERKEL, Examiners.

1. THE METHOD FORMING A HOT DUCTILE SHEET OF THERMOPLASTIC MATERIAL INTO A THREE DIMENSIONAL SHAPE COMPRISING FORMING THE MATERIAL INTO A CAVITY MOLD INCLUDING THE STEPS OF PLACING THE MATERIAL OVER THE MOUTH OF A CAVITY MOLD, PROVIDING A HEAT SOURCE OVER THE MOLD, APPLYING PRESSURE TO CAUSE AN AREA OF THE MATERIAL TO MOVE UPWARDLY FROM THE CAVITY MOLD SO AS TO PROGRESSIVELY COME IN CONTACT WITH SURFACES OF THE HEAT SOURCE, AND THEN APPLYING PRESSURE TO FORCE THE SAID AREA OF THE MATERIAL DOWNWARD TO CONFORM TO THE SHAPE OF THE CAVITY MOLD WHEREBY THE HEATING OF THE AREA AS IT IS MOVED UPWARDLY IS DETERMINED BY ITS CONTACTING OF THE HEATED SURFACES SO THAT THERE IS GREATER HEATING OF THE AREA ADJACENT THE RIM OF THE CAVITY MOLD WHEREBY A FORMED ARTICLE IS REALIZED HAVING BOTTOM AND SIDE WALLS OF CONTROLLED THICKNESS DISTRIBUTION. 